/*
 * binaryheap.h
 *
 * A simple binary heap implementation
 *
 * Portions Copyright (c) 2012-2017, PostgreSQL Global Development Group
 *
 * src/include/lib/binaryheap.h
 */

#ifndef BINARYHEAP_H
#define BINARYHEAP_H

/*
 * For a max-heap, the comparator must return <0 iff a < b, 0 iff a == b,
 * and >0 iff a > b.  For a min-heap, the conditions are reversed.
 */
typedef int (*binaryheap_comparator) (Datum a, Datum b, void *arg);

/*
 * binaryheap
 *
 *        bh_size            how many nodes are currently in "nodes"
 *        bh_space        how many nodes can be stored in "nodes"
 *        bh_has_heap_property    no unordered operations since last heap build
 *        bh_compare        comparison function to define the heap property
 *        bh_arg            user data for comparison function
 *        bh_nodes        variable-length array of "space" nodes
 */
typedef struct binaryheap
{
    int            bh_size;
    int            bh_space;
    bool        bh_has_heap_property;    /* debugging cross-check */
    binaryheap_comparator bh_compare;
    void       *bh_arg;
    Datum        bh_nodes[FLEXIBLE_ARRAY_MEMBER];
} binaryheap;

extern binaryheap *binaryheap_allocate(int capacity,
                    binaryheap_comparator compare,
                    void *arg);
extern void binaryheap_reset(binaryheap *heap);
extern void binaryheap_free(binaryheap *heap);
extern void binaryheap_add_unordered(binaryheap *heap, Datum d);
extern void binaryheap_build(binaryheap *heap);
extern void binaryheap_add(binaryheap *heap, Datum d);
extern Datum binaryheap_first(binaryheap *heap);
extern Datum binaryheap_remove_first(binaryheap *heap);
extern void binaryheap_replace_first(binaryheap *heap, Datum d);

#define binaryheap_empty(h)            ((h)->bh_size == 0)

#endif                            /* BINARYHEAP_H */
